1. Field of the Invention:
This invention relates to novel compositions which exhibit both corrosion and scale inhibition. More specifically, this invention relates to a combined corrosion and scale inhibitor synthesized from the reaction of a heterocyclic nitrogen containing compound with an aldehyde and phosphorus acid constituent.
2. Description of the Prior Art:
It is generally recognized and widely known that both metal corrosion and mineral scale deposition are serious operational problems in many industries and are particularly severe in the oil and gas producing, refining and transportation industry. By far, most internal corrosion of metal equipment occurs in the presence of liquid water, even in systems handling primarily hydrocarbons. Corrosion attack results most often from chemical reactions of the metal with oxygen, hydrogen sulfide and carbon dioxide dissolved in the water. Certain salts and minerals also present in the water contribute to the corrosion process. Some dissolved mineral constituents, specifically calcium, barium, strontium, bicarbonate, carbonate and sulfate ions, also react to form troublesome mineral scales that clog the tubulars and process vessels and impede heat transfer. The combined costs from equipment replacement, repair, cleaning and downtime caused by corrosion and scaling in the United States can be measured in terms of billions of dollars each year. Such costs are kept at acceptable levels by several techniques, including additions of chemical inhibitors which slow the corrosion attack and scale accumulation. Unfortunately, most corrosion inhibitors such as the organic amines are not effective as scale inhibitors. Conversely, most scale inhibitors, such as the various phosphorus containing chemicals (phosphates, phosphonates and phosphate esters) are not effective alone in preventing corrosion, especially that caused by hydrogen sulfide and carbon dioxide. Consequently, it is common practice to apply at least two types of inhibitors to systems effected by both corrosion and scale. The individual corrosion and scale inhibitors generally have to be applied separately for best control and effectiveness. Thus, many attempts have been made to create a single inhibitor composition to control both scaling and corrosion conditions with a single treatment.
For example, U.S. Pat. No. 3,770,815 describes one such composition that is oil soluble. However, these previous dual purpose compositions have not adequately solved the problem and the so-called "combination" corrosion/scale inhibitors are used to a relatively limited extent, in that they make up only a small fraction of the total inhibitor sales. A particularly severe shortcoming of most combination corrosion/scale inhibitors currently available is that they are not capable of adequately preventing the severe corrosion which results from the simultaneous presence of oxygen and hydrogen sulfide. This is essentially an unsolved problem in the oil field water systems handling sour brines that are contaminated by atmospheric oxygen. Further, the presently available combination inhibitor products are almost universally less effective at equal concentrations than are the commercial single purpose scale inhibitors and therefore, must be used at higher treating levels.
The present invention provides in a single chemical composition a water soluble inhibitor that is highly effective in preventing corrosion by oxygen and hydrogen sulfide, either singularly or in combination, and which is equivalent in scale inhibiting efficiency to the single purpose scale inhibitors now used.